The process of compressing an audio source, such as voice or music, and storing it digitally in a file is conventionally known. A user connected to the Internet can selectively download an encoded compressed file, such as a file in the MP3 format, run software to decode the file and thereby listen to the audio source. The MP3 format is well known in the art and refers to Layer 3 audio files of the Motion Picture Experts Group (MPEG) international standard for representation, compression, and decompression of motion pictures and associated audio on digital media. Conventionally, a decoder is employed to decode the encoded digital audio file.
A drawback of conventional methods is that compressed audio files do not include information and links to Internet documents that can be viewed during audio playback. Conventional methods require the listener of the decoded audio file to manually make any such links to Internet documents.
Methods are known for embedding data at a predetermined point in a media file, which may include, but is not limited to, an audio file. Such methods provide a means of permanently embedding data in a media file, extracting and displaying or further processing the embedded data on a suitable decoding system. For example, an Internet Uniform Resource Locator (URL) link to “www.intervideo.com/promotion.htm” can be embedded in a music file. Using these methods, whenever the music file is decoded and played, the corresponding decoder application can enable the web page corresponding to the embedded link to display a promotional message at a point in time during playback of the music file. For another example, a promotional message can be embedded in a music file such that when the music is decoded and played, the corresponding decoder application enables display of the message at a point in time in the middle of a particular song being played back. A drawback with these methods is that the embedded data permanently remains in the file and the decoder will always try to display the information. For the first above example, if the web page “promotion.htm” is removed from the web site “www.intervideo.com”, the conventional decoder tries to load that page at a point in time during playback and will always display an error or a default message to indicate that the decoder could not find or display the information. For a further example, if the following text “Buy this CD now to get 50% discount” is embedded in a song to promote a limited duration discount offer, the text will be displayed every time the song is played back, even after the discount offer has expired.
One way to address the above drawbacks is to specify the offer duration in the message, for example, by changing the text to read “Buy this CD now to get 50% discount, offer expires on Jun. 25th, 2001 at midnight”. Even though this solves the ambiguity of offer duration, the message will still be displayed permanently at a point in time during playback even years after the offer has expired. Another approach is to remove the embedded data after a certain amount of time, but this entails altering the media file, which requires additional processing and may not be desirable or feasible. A similar problem exists when the intention is to display the information only after a certain date.
What is needed is a method whereby information embedded in a media file can be extracted only during a predetermined time duration.